In city centers, the damage caused by inundation is aggravated by rising populations and urbanization, which extend impermeable areas. Research is needed to identify the inundation risks caused by climate change and quantitatively assess the consequences. In this study, we proposed an improved reliability study which considers resilience in the original evaluation method for the reliability of a storm sewer network. Rainfall-runoff analysises were performed on a part of Bangbae 2 drainage basin in Seoul by applying Storm Water Management Model 5 Ver. Based on the results of the application of excessive rainfall events, the original reliability evaluation method was compared with the improved reliability evaluation method. Consequently, the effect of the improvement of the cluster about 30% was confirmed when selection the central value rather than the existing representative value. The improved reliability evaluation method proposed in this study can be used as a design objective function and as an index for evaluating the inundation risk in adjacent drainage basins.